Color television tube fabrication

ABSTRACT

IN THE PROCESS OF FORMING COLOR TELEVISION TUBE FACEPLATES THE IMPROVEMENT WHICH COMPRISES COATING A CATHODE RAY TUBE FACEPLATE WITH A SOLID LDIGHT-SENSITIVE LAYER CAPABLE OF DEVELOPING A RDP OF 0.2 TO 2.2; EXPOSING SAID LIGHT-SENSITIVE ORGANIC LAYER IN PREDETERMINED AREAS, CORRESPONDING TO THE PREDETERMINED CATHODOLUMINSCENT AREAS OF A FACEPLATE, TO ACTINIC RADIATION IN IMAGE RECEIVING MANNER TO ESTABLISH TO POTENTIAL RDP OF 0.2 TO 2.2; APPLYING TO SAID ORGANIC LAYER, FREE FLOWING POWDER PARTICLES COMPRISING AT LEAST ONE LIGHTABSORBING PIGMENT, SAID FREE FLOWING POWDER HAVING A DIAMETER ALONG AT LEAST ONE AXIS OF AT LEAST ABOUT 0.3 MICRON BUT LESS THAN 25 TIMES THE THICKNESS OF SAID ORGANIC LAYER; WHILE THE LAYER IS AT A TEMPERATURE BELOW THE MELTING POINT OF THE POWDER PARTICLES AND OF THE ORGANIC LAYER, PHYSICALLY EMBEDDING SAID POWDER PARTICLES AS A MONOLAYER IN THE STRATUM AT THE SURFACE OF SAID LIGHT-SENSITIVE LAYER TO YIELD AN IMAGE HAVING PORTIONS VARYING IN DENSITY IN PROPORTION TO THE EXPOSURE OF EACH PORTION; AND REMOVING NON-EMBEDDED PARTICLES FROM SAID ORGANIC LAYER TO DEVELOP A DISCRETE PATTERN OF POWDER PARTICLES COMPRISING AT LEAST ONE LIGHT-ABSORBING PIGMENT.

United States Patent "ice 3,676,127 COLOR TELEVISION TUBE FABRICATION Thomas F. Protzman, Worthington, Ohio, and William H. Magidson, Decatur, 11]., assignors to A. E. Staley Manufacturing Company, Decatur, Ill. No Drawing. Filed Jan. 23, 1970, Ser. No. 5,363 Int. Cl. G03c 5/ 00, 5/04 US. Cl. 9636.1 1 Claim ABSTRACT OF THE DISCLOSURE In the process of forming color television tube faceplates the improvement which comprises coating a cathode ray tube faceplate with a solid, light-sensitive layer capable of developing a R of 0.2 to 2.2; exposing said light-sensitive organic layer in predetermined areas, corresponding to the predetermined cathodoluminescent areas of the faceplate, to actinic radiation in image receiving manner to establish a potential 'R of 0.2 to 2.2; applying to said organic layer, free flowing powder particles comprising at least one lightabsorbing pigment, said free flowing powder having a diameter along at least one axis of at least about 0.3 micron but less than times the thickness of said organic layer; while the layer is at a temperature below the melting point of the powder particles and of the organic layer, physically embedding said powder particles as a monolayer in the stratum at the surface of said light-sensitive layer to yield an image having portions varying in density in proportion to the exposure of each portion; and removing non-embedded particles from said organic layer to develop a discrete pattern of powder particles comprising at least one light-absorbing pigment.

This invention relates to methods of forming color television tube faceplates. More particularly, this invention relates to methods for fabricating screens for color television tubes wherein a powder comprising at least one light-absorbing pigment is deposited on the tube face in predetermined phosphor free areas as an intermediate step in the fabrication of such screens.

Image display screens for cathode ray tubes of the type adapted to be employed in color television viewing apparatus conventionally comprise a transparent viewing panel having a vast number of similar patterns discretely formed thereon. Each of the patterns may consist of groups of stripes, bars or dots of red-emitting, green-emitting and blue-emitting cathodoluminescent materials capable of color fluorescence under electron beam bombardment. A multi-colored cathode ray tube screen of this type is generally fabricated by sequential photographic printing procedures wherein a separate application of negative acting photosensitized material or resist is used to secure each of the specific color-emitting fluorescent materials to the internal concave face of the viewing panel. For example, in fabricating a dotted color screen by this process, a thin layer of a negative acting photosensitized substance and one of the fluorescent materials is deposited on the concave surface of the faceplate and discretely exposed to light irradiation directed through an appropriate negative or shadow mask from a point source approximating the location, relative to the support, that the electron gun associated with this particular phosphor will occupy in the finished tube, thereby causing the light impinged photosensitized substance to harden and adhere to the panel as a multitude of dot-like areas. The portions of the screen which are unexposed to light are not substantially hardened and are subsequently removed by dissolving the unhardened substance with a suitable solvent and rinsing same from the panel surface. The unexposed radiationsensitive binder and phosphor adhering thereto are 3,676,127 Patented July 11, 1972 removed in this way leaving a plurality of discrete elements on the screen. This procedure is repeated in forming the second and third color-emitting cathodoluminescent areas by utilizing, in each case, a new layer of negative acting photosensitized material, different color-emitting phosphor and a differently orientated light source thereby providing a resultant multitude of adjacently related color triads comprising the screen of the tri-color picture tube viewing panel. A subsequent bakeout or firing disposes of the volatile ingredients leaving the phosphor pattern screen as a complete unit.

The phosphor areas of tri-color picture tube faceplates prepared in this manner cover about 50% of the faceplate viewing area. In order to provide maximum contrast during viewing, particularly for daytime viewing, it is necessary to minimize or eliminate the reflection of external room light at the internal surface of the television tube. Accordingly, faceplates are generally fabricated from glass, which only transmits about 40 to 50% of the light striking the glass, as opposed to window glass, which transmits about 90% of the light. However, this in effect, cuts the efiiciency of the phosphors on the surface of the faceplate in half. Theoretically, faceplates capable of transmitting to light could be used if the spaces between the phosphors was covered with light-absorbing pigment or pigments. The production of faceplates of this type is complicated by the fact that light-sensitive resist formers are generally negative acting, i.e., the exposed areas are hardened, and by the fact that television tube manufacturers prefer to expose the light-sensitive negativeacting material through the shadow mask subsequently used in the assembled tube. Accordingly, there is a need for positive acting systems capable of depositing lightabsorbing pigments on the surface of color television tube faceplates in the phosphor-free areas.

The general object of this invention is to provide a method of depositing light-absorbing pigment or pigments onto predetermined phosphor-free areas of a faceplate using a positive acting light-sensitive system. Another object of this invention is to provide a method of depositing light-absorbing pigment or pigments onto predetermined phosphor-free areas of a faceplate by a photographic printing procedure wherein all light irradiation is through a shadow mask. Other objects will appear hereinafter.

In the description that follows, the phrase powderreceptive, solid, light-sensitive organic layer is used to describe an organic layer which is capable of developing a predetermined contrast or reflection density (R upon exposure to actinic light and embedrnent of black powder particles of a predetermined size in a single stratum at the surface of said organic layer. While explained in greater detail below, the R of a light-sensitive layer or R of a postive acting light-sensitive layer are photometric measurements of the difference in degree of blackness of undeveloped areas and black powder developed areas. The terms physically embedded or physical force are used to indicate that the powder particle is subjected to an external force other than, or in addition to, either electrostatic force or gravitational force resulting from dusting or sprinkling powder particles on a substrate. The terms mechanically embedded or mechanical force are used to indicate that the powder particle is subjected to a manual or machine force, such as lateral to-and-fro or cir cular rubbing or scrubbing action. The term embedded is used to indicate that the powder particle displaces at least a portion of the light-sensitive layer and is held in the depression so created, i.e., at least a portion of each particle is below the surface of the light-sensitive layer.

The objects of this invention can be attained by coating a cathode ray tube faceplate with a solid, light-sensitive organic layer capable of developing a R of 0.2 to 2.2, preferably 0.4 to 2.0; exposing said light-sensitive organic layer in predetermined areas, corresponding to the predetermined cathodoluminescent areas of the faceplate, to actinic radiation in image-receiving manner to establish a potential R of 0.2 to 2.2; applying to said layer of organic material, free flowing powder particles comprising at least one light absorbing pigment, said free flowing powder having a diameter, along at least one axis of at least about 0.3 micron but less than 25 times the thickness of said organic layer; while the layer is at a temperature below the melting points of the powder particles and of the organic layer, physically embedding said powder particles as a monolayer in a stratum at the surface of said light-sensitive layer to yield an image having portions varying in density in proportion to the exposure of each portion; and removing non-embedded particles from said organic layer to develop a discrete pigment pattern When the light-sensitive organic layer is irradiated through a shadow mask, which is to be used in the finished tube, the irradiation should come from point sources approximating the locations, relative to the support, that the electron guns associated with the phosphors in a tri-color television tube occupy in the finished tube. In general, when using a shadow mask, it is preferred to employ three separate exposure steps in order to utilize the conventional exposure equipment currently being used by color television manufacturers. However, it is possible to expose from three point light sources simultaneously. Since the light-sensitive organic layers employed in this invention to deposit the light absorbing pigments are positive acting, the exposed portions will not accept the developing powders containing the light absorbing pigments and the developing powders are only deposited in the predetermined phosphor free areas. For the purposes of this invention, the phosphors may be deposited by conventional means either before or after the deposition of the light-absorbing pigment or if desired the light absorbing pigments can be deposited after one or two of the cathodoluminescent phosphors have been deposited and prior to the third phosphor. The faceplate can be fired after the light absorbing pigments and phosphors have been deposited on the surface of the faceplate.

{The present invention provides a method of depositing a light absorbing pigment on the phosphor free areas of a faceplate where the image is developed by embedding powder particles comprising a pigment of predetermined size into a stratum at the surface of a positive acting powder-receptive solid, light-sensitive organic layer. This process makes use of the phenomena that thin layers of many solid organic layers, some in substantially their naturally occurring or manufactured forms and others including additives to control their powder receptivity and/or sensitivity to actinic radiation, can have surface properties that can be varied within a critical range by exposure to actinic radiation between a particle-receptive condition and a particle-non-receptive condition. As explained below, the particle receptivity and particle noneceptivity of the solid thin layers are dependent on the size of the particles, the thickness of the solid thin layer and development conditions, such as layer temperature.

Broadly speaking, the present method of depositing powder images differs from known methods in various subtle and unobvious ways. For example, the powder particles that form the image are not merely dusted on, but instead are applied against the surface of the light-sensitive organic layer under moderate physical force after exposing the light-sensitive layer to actinic radiation. The relatively soft or particle-receptive nature of the light-sensitive layer is such that substantially a monolayer of particles, or isolated small agglomerates of a predetermined size, are at least partially embedded at the surface of the light-sensitive la'yer by moderate physical force. The surface condition in the particle receptice area is at most only slightly 4 soft but not fluid as in prior processes. The relatively hard or particle non-receptive condition of the light-sensitive surface in the non-image areas is such that when powder particles of a predetermined size are applied under the same moderate physical force few, if any, are embedded sufliciently to resist removal by moderate dislodging action such as blowing air against the surface. Any particles remaining in the non-image areas are removed readily by rubbing a soft pad over the surface For use in this invention, the solid, light-sensitive organic layer, which can be an organic material in its naturall'y occurring or manufactured form or a mixture of said organic material with plasticizers and/ or photoactivators for adjusting the powder receptivity and sensitivity to actinic radiation, must be capable of developing a predetermined contrast or R using a suitable black developing powder under the conditions of development. The powder-receptive areas of the unexposed, positiveacting, light-sensitive layer must have a softness such that suitable particles can be embedded into a stratum at the surface of the light-sensitive layer by mild physical forces. However, the layer should be hard and non-sticky. The film should also have a degree of toughness so that it maintains its integrity during development. If the R of the light-sensitive layer is below about 0.2, the lightsensitive layer is too hard to accept a suitable concentration of particles. On the other hand, if the R is above about 2.2, the light-sensitive is so soft that it is difficult to maintain film integrity during physical development. Further, if the R, is above 2.2, the light-sensitive layer is so soft that more than one layer of powder particles may be deposited with attendant loss of image fidelity and the layer may be displaced by mechanical forces resulting in the distortion or destruction of the image. Accordingly, for use in this invention the light-sensitive layer must be capable of developing a R within the range of 0.2 to 2.2 or preferably 0.4 to 2.0 using a suitable black developing powder under the conditions of development.

The R of the positive acting light-senstiive layer, which can be called R is a photometric measurement of the reflection density of a black-powder developed light-sensitive layer after a positive-acting, light-sensitive layer has been exposed to sufiicient actinic radiation to convert the exposed areas into a substantially powder-non-receptive state (clear the background). The reflection density of the solid, positive-acting, light-sensitive layer (R is determined by coating the light-sensitive layer on a white substrate, exposing the light-sensitive layer to suflicient actinic radiation image-wise to clear the background of the solid positive-acting light-sensitive layer, applying a black powder (prepared from 77% Pliolite VTL and 23% Neo Spectra carbon black in the manner described below) to the exposed layer, physically embedding said black powder under the conditions of development as a monolayer in a stratum at the surface of said light-sensitive layer and removing the non-embedded particles from said light-sensitive layer. The developed organic layer containing black powder embedded image areas and substantially powder free non-image areas is placed in a standard photometer having a scale reading from 0 to reflection of incident light or an equivalent density scale, such as on Model 500A photometer of the Photovolt Corporation. The instrument is zeroed (0 density; 100% reflectance) on a powder free non-image area of the light-sensitive organic layer and an average R reading is determined from the powder developed area. The reflection density is a measure of the degree of blackness of the developed surface which is relatable to the concentration of particles per unit area. If the R under the conditions of development is between 0.2 (63.1% reflectance) and 2.2 (0.63% reflectance), or preferably between 0.4 (39.8% reflectance) and 2.0 (1.0% reflectance), the solid, lightsensitive organic material deposited in a layer is suitable for use in this invention.

Although the R of all light-sensitive layers is determined by using the aforesaid black developing powder and a white substrate, the R is only a measure of the suitability of a light-sensitive layer for use in this invention.

Since the R of any light-sensitive layer is dependent on numerous factors other than the chemical constitution of the light-sensitive layer, the light-sensitive layer is best defined in terms of its R under the development conditions of intended use. The positive-acting, solid, light-sensitive organic layers useful in this invention must be powder receptive in the sense that the aforesaid black developing powder can be embedded as a mono-particle layer into a stratum at the surface of the unexposed layer to yield a R of 0.2 to 2.2(0.4 to 2.0 preferably) under the predetermined conditions of development and light-sensitive in the sense that upon exposure to actinic radiation the most exposed areas can be converted into the non-particle receptive state, background cleared (under the predetermined conditions of development. In other words, the positiveacting, light-sensitive layer must contain a certain inherent powder receptivity and light-sensitivity. The positive-acting, light-sensitive layers are apparently converted into the powder-non-receptive state by a light-catalyzed hardening action, such as photopolymerization, photocross-linking, photooxidation, etc. Some of the photohardening reactions are dependent on the presence of oxygen, such as the photooxidation of internally ethylenically unsaturated acids and esters while others are inhibited by the presence of oxygen, such as those based on the photopolymerization of the vinylidene groups of polyvinylidene monomers alone or together with polymeric materials. The latter require special precautions, such as storage in oxygen-free atmosphere or oxygen-impermeable cover sheets. For this reason, it is preferable to use solid, positive-acting, filmforming, organic materials, containing no terminal ethylenic unsaturation.

In general, the positive-acting, solid, light-sensitive layers useful in this invention comprise a film-forming organic material in its naturally occurring or manufactured form or a mixture of said organic material with plasticizers and/or photoactivators for adjusting powder receptivity and sensitivity to actinic radiation. Suitable positive-acting, film-forming organic materials, which are not inhibited by oxygen, include internally ethylenically unsaturated acids, such as abietic acid, rosin acids, partially hydrogenated rosin acids, such as those sold under the name Staybelite resin, wood rosin, etc., esters of internally ethylenically unsaturated acids, methylol amides of maleated oils such as described in application Ser. No. 643,367 filed June 5, 1967, now Pat. No. 3,471,466 phosphatides of the class described in application Ser. No. 796,841 now Pat. No. 3,585,031 filed on Feb. 5, 1969 in the name of Hayes, such as soybean lecithin, partially hydrogenated lecithin, dilinolenyl-alpha-lecithin, etc., partially hydrogenated rosin acid esters, such as those sold under the name Staybelite esters, rosin modified alkyds, etc.; polymers of ethylenically unsaturated monomers, such as vinyltoluene-alpha methyl styrene copolymers, polyvinyl cinnamate, polyethyl methacrylate, vinyl acetate-vinyl stearate copolymers, polyvinyl pyrrolidone, etc.; coal tar resins, such as coumarone-indene resins, etc.; halogenated hydrocarbons, such as chlorinated waxes, chlorinated polyethylene, etc. Positive acting, light-sensitive materials, which are inhibited by oxygen include mixtures of polymers, such as polyethylene terephthalate/sebacate, or cellulose acetate or acetate/butyrate, with polyunsaturated vinylidene monomers, such as ethylene glycol diacrylate or dimethacrylate, tetraethylene glycol diacrylate or dimethacrylate, etc.

Although numerous positive-acting, film-forming organic materials have the requisite light-sensitivity and powder receptivity at predetermined development temperatures, it is generally preferable to compound the film-forming organic material with photoactivator(s) and/or plasticizer (s) to impart optimum powder receptivity and lightsensivit'y to the light-sensitive layer. In most cases, the light-sensivity of an element can be increased many fold by incorporation of a suitable photoactivator capable of producing free-radicals, which catalyze the light-sensitive reaction and reduce the amount of photons necessary to yield the desired physical change.

Suitable photoactivators capable of producing freeradicals include benzil, benzoin, Michlers ketone, diacetyl, phenathraquinone, p-dimethylaminobenzoin, 7,8-benzoflavone, trinitrofluorenone, desoxybenzoin, 2,3-pentanedione, dibenzylketone, nitroisatin, di(6-dimethylamino-3- pyradil)methane, metal naphanates, N-methyl-N-phenylbenzylamine, pyridil, 5-7 dichloroisatin, azodiisobutyronitrile, trinitroanisole, chlorophyll, isatin, bromoisatin, etc. These compounds can be used in a concentration of .001 to 2 times the weight of the film-forming organic material (.1%-200% the weight of film former). As in most catalytic systems, the best photoactivator and optimum concentration thereof is dependent upon the film-forming organic material. Some photoactivators respond better with one type of film former and may be useful over rather narrow concentration ranges whereas others are useful with substantially all film-formers in wide concentration ranges.

The acyloin and vicinal diketone photoactivators, particularly benzil and benzoin are preferred. Benzoin and benzil are effective over wide concentration ranges with substantially all film forming light-sensitive organic materials. Benzoin and benzil have the additional advantage that they have a plasticizing or softening effect on film-forming light-sensitive layers, thereby increasing the powder receptivity of the light-sensitive layers. When employed as a photoactivator, benzil should preferably comprise at least 1% by Weight of the film-forming organic material (.01 times the film former weight).

Dyes, optical brighteners and light absorbers can be used alone or preferably in conjunction with the aforesaid free-radical producing photoactivators (primary photoactivators) to increase the light-sensitivity of the light-sensitive layers of this invention by converting light rays into light rays of longer lengths. [For convenience, these secondary photoactivators (dyes, optical brighteners and light absorbers) are called superphotoacti'vators. Suitable dyes, optical brighteners and light absorbers include 4 methyl-7-dimethylaminocoumarin, Calcofiuor yellow HEB (preparation described in US. Pat. 2,415,- 373), Calcofluor white SB super 30080, Calcofluor, Uvitex W conc., Uvitex TXS conc., Uvitex RS (described in Textil-Rundschau 8 (1953, 339'), Uvitex WGS conc.,

Uvitex K, 'Uvitex CF conc., Uvitex W (described in Textil-Rundschau 8, (1953), 340), Aclarat 8678, Blancophor OS, Tenopol UNPL, MDAC 8-8844, Uvinul 400, Thilflavin TGN conc., Aniline yellow-S (low conc.), Seto flavine T 5506-140, Auramine O, Calcozine yellow OX, Calcofluor RW, Calcofiuor GAC, Acetosol yellow 2 RLS-RHF, Eosine bluish, Chinoline yellow-P conc., Ceniline yellow S (high conc.), Anthracene blue Vio'let fluorescence, Calcofluor white MR, Tenopol PCR, Uvitex GS, Acid-yellow-T-supra, Acetosol yellow 5 GLS, Calcocid OR, Y, Ex. Conc., diphenyl brilliant flavine 7 GFF, Resoflorm fluorescent yellow 3 GPI, Eosin yellowish, Thiazole fluorescor G, Pyrazalone organe YB-3, and National FD'&C yello w. Individual superphotoactivators may respond better with one type of light-sensitive organic film-former and photoactivator than with others. Further, some photoactivators function better with certain classes of brighteners, dyes and light absorbers. For the most part, the most advantageous combinations of these materials and proportions can be determined by simple experimentation.

As indicated above, plasticizers can be used to impart optimum powder receptivity to the light-sensitive layer. With the exception of lecithin, most of the filmforming light-sensitive organic materials useful in this invention are not powder-receptive at room temperature 7 but are powder-receptive above room temperature. Accordingly, it is desirable to add suflicient plasticizer to impart room temperature (15 to 30 C.) or ambient temperature powder receptivity to the light-sensitive layers and/or broaden the R range of the light-sensitive layers.

-While various softening agents, such as dimethyl siloxanes, dimethyl phthalate, glycerol, vegetable oils, etc. can be used as plasticizers, benzil and benzoin are preferred since, as pointed out above, these materials have the additional advantage that they increase the lightsensitivity of the film-forming organic materials. As plasticizer-photoactivators, benzoin and benzil are preferably used in a concentration of 1% to 80% by weight of the film-forming solid organic material.

The preferred positive-acting light-sensitive filmv formers containing no conjugated terminal ethylenic unsaturation include the esters and acids of internally ethylenically unsaturated acids, particularly the phosphatides, rosin acids, partially hydrogenated rosin acids and the partially hydrogenated rosin esters. These materials, when compounded with suitable photoactivators, preferably acyloins or vicinal diketones together with superphotoactivators require less than 5 minutes exposure to clear the background of light-sensitive layers and can be developed to yield light-absorbing pigment patterns having the desired configuration.

In somewhat greater detail, the inner or concave surface of a cathode ray tube faceplate, is first thoroughly cleaned. The cleaning may be accomplished by successive rinses of alcohol followed by rinses of distilled or deionized water. Rinses with a mildly alkaline solution followed by a rinse with a weak acidic solution are also effective; however, thorough rinsing with distilled or deionized water should follow any of the above procedures. if an acid bath containing halogen ions is utilized the rinsing should be sufiicient to insure removal thereof since these extremely reactive ions tend to poison the subsequently applied phosphor.

The solid, light-sensitive film-forming organic layer capable of developing a R of 0.2 to 2.2 can be applied to the faceplate by spraying, whirler coating from solvent solution, coating the faceplate with solvent solution, etc. The light-sensitive material is preferably applied by spraying upwardly to the support and the coating is built up gradually by successive passes of spray rather than singly. The multiple spraying allows a more uniform coating to be applied. Unlike other processes, which are dependent upon maintaining a certain level of tackiness, the coating operation can be performed at almost any temperature and humidity.

The light-sensitive layer must be at least 0.1 micron thick, and preferably at least 0.4 micron, in order to hold powders during development. If the light-sensitive layer is less than 0.1 micron, or the powder diameter is more than 25 times layer thickness, the light-sensitive layer does not hold the powder with the necessary tenacity. In general, as layer thickness increases, the light-sensitive layer is capable of holding larger particles. However, as the light-sensitive layer thickness increases, it becomes increasingly difficult to maintain film integrity during development. Accordingly, the light-sensitive layer must be from 0.1 to 40 microns, preferably from 0.4 to microns.

The light-sensitive layers of predetermined thickness are preferably applied to the faceplate from an organic solvent (hydrocarbon, such as hexane, heptane, benzene, etc.; halogenated hydrocarbon, such as chloroform, carbon tetrachloride, 1,1,1-trichloroethane, trichloroethylene, etc.). If desired, the light-sensitive layers can be deposited from suitable aqueous emulsions. The thickness of the light-sensitive layer can be varied as a function of the concentration of the solids dissolved in the solvent.

After the faceplate is coated with a suitable solid, lightsensitive organic layer, a latent image is formed by exposing the element to actinic radiation in image receiving manner for a time sufficient to provide a potential R of 0.2 to 2.2 (clear the background of the positive-acting, light-sensitive layers). Although the light-sensitive elements can be exposed to actinic light through a photographic negative, it is preferred to employ a shadow mask. When using a shadow mask, it is generally desirable to expose the light-sensitive layer to irradiation from point light sources approximating the locations, relative to the support, that the electron guns associated with the phosphors will occupy in the finished tube.

As indicated, the latent images are produced from the positive-acting, light-sensitive layers by exposing the element in image-receiving manner for a time suflicient to clear the background, i.e., render the exposed areas nonpowder receptive. To some extent, the amount of actinic radiation necessary to clear the background varies with developer powder size and development conditions. Due to these variations, it is sometimes desirable to slightly over-expose to assure complete clearing of the background and prevent contamination of the phosphorluminescent areas.

After the light-sensitive element is exposed to actinic radiation for a time sufficient to clear the background of the positive-acting light-sensitive layer in the predetermined phosphor free areas, a powder comprising a light absorbing pigment or pigments is applied to the lightsensitive layer. The powder, which has a diameter or dimension along one axis of at least 0.3 micron, is applied physically with a suitable force, preferably mechanically, to embed the powder in the light-sensitive layer. The developing powder can be virtually any shape, such as spherical, acicular, platelets, etc. provided it has a diameter along at least one axis of at least 0.3 micron.

The light-absorbing pigment powders, which are preferably black or mixtures of pigments simulating black, can be applied in a substantially pure form or on a suitable carrier. Carriers, such as resinous or polymeric materials, can be employed to regulate the particle size of the lightabsorbing pigment and/or to apply more pigment. The pigment can be ball-milled with polymeric carrier in order to coat the carrier with pigment or, if desired, the pigment can be blended above the melting point of resinous carrier, ground to a suitable size and classified. Suitable black pigments include graphite, carbon black, manganese dioxide black, ferric oxide black, etc.

The black developing powder for determining the R; of a light-sensitive layer, which can also be employed as a suitable light-absorbing pigment in this invention is formed by heating about 77% Pliolite VTL (vinyltoluenebutadiene copolymer) and 23% Neo Spectra carbon black at a temperature above the melting point of the resinous carrier, blending on a rubber mill for fifteen minutes and then grinding in a Mikro-atomizer.

The developing powders useful in this invention contain particles having a diameter or dimension along at least one axis from 0.3 to 40 microns, preferably from 0.5 to 10 microns, with powders of the order of 1 to 15 microns being best for light-sensitive layers of 0.4 to 10 microns. Maximum particle size is dependent on the thickness of light-sensitive layer while minimum particle size is independent of layer thickness. Electron microscope studies have shown that powders having a diameter 25 times the thickness of the light-sensitive layer cannot be permanently embedded into light-sensitive layers and, generally speaking, best results are obtained where the diameter of the powder particle is less than about 10 times the thickness of the light-sensitive layer. For the most part, particles over 40 microns are n't detrimental to image development provided the developing powder contains a reasonable concentration of powder particles under 40 microns, which are less than 25 times, and preferably less than 10 times, the light-sensitive layer thickness.

Although developing powders over 40 microns are not detrimental to image development, the presence of particles under 0.3 micron diameter along all axes can be detrimental. In general, it is preferable to employ developing powders having substantially all powders having a diameter along at least one axis not less than 0.3 micron, preferably more than 0.5 micron, since particles less than 0.3 micron tend to embed in non-image areas. As the particle size of the smallest powder in the developer increases, less exposure to actinic radiation is required to clear the background.

For best results, the developing powder, which comprises a light absorbing pigment, should have substantially all particles (at least 95% by weight) over 1 micron in diameter along one axis and preferably from 1 to 15 microns for use with light-sensitive layers of from 0.4 to microns. In this way, powder embedment in image areas is maximum.

In somewhat greater detail, the developing powder is applied directly to the light-sensitive layer, while the powder receptive areas of said layer are in at most only a slightly soft condition and said layer is at a temperature below the melting point of the layer and powder. The powder is distributed over the area to be developed and physically embedded into the stratum at the surface of the light-sensitive layer, preferably mechanically by force having a lateral component, such as to-and-fro and/or circular rubbing or scrubbing action using a soft pad, fine brush or even an inflated balloon. If desired, the powder may be applied separately or contained in the pad or brush. The quantity of powder is not critical provided there is an excess available beyond that required for full development of the area, as the development seems to depend primarily on particle-to-particle interaction rather than brush-tosurface or pad-to-surface forces to embed a layer of powder particles substantially one particle thick (monoparticle layer) into a stratum at the surface of the lightsensitive layer. Only a single stratum of powder particles penetrates into the powder-receptive areas of the lightsensitive layer even if the light-sensitive layer is several times thicker than the developer particle diameter.

The pad or brush used for development is critical only to the extent that it should not be so stiif as to scratch or scar the film surface when used with moderate pressure with the preferred amount of powder to develop the film. Ordinary absorbent cotton loosely compressed into a pad about the size of a baseball and Weighing about 3 to 6 grams is especially suitable. The developing motion and force applied to the pad during development is not critical. The speed of the swabbing action is not critical other than that it affects the time required; rapid movement requiring less time than slow. The preferred mechanical action involved is essentially the lateral action applied in ultrafine finishing of a wood surface by hand sanding or steel wooling.

Hand swabbing is entirely satisfactory, and when performed under the conditions described above, will reproducibly produce the maximum density which the material is capable of achieving. That is, the maximum concentration of particles per unit area will be deposited under the prescribed conditions, dependent upon the physical properties of the material such as softness, resiliency, plasticity, and cohesivity. Substantially the same results can be achieved using a mechanical device for the powder application. A rotating or rotating and oscillating, cylindrical brush or pad may be used to provide the described brushing action and will produce a substantially similar end result.

After the application of developing powder, excess powder remains on the surface which has not been sulficiently embedded into, or attached to, the faceplate. This may be removed in any convenient way, as by wiping with a clean pad or brush usually using somewhat more force than employed in mechanical development, by vacuuming, by vibrating, by air doctoring, by air jets, etc., and recovered. For simplicity and uniformity of results, the excess powder usually is blown 01f using an air gun having an air-line pressure of about 2.0 to 40 p.s.i. The gun is preferably held at an angle of about 30 to 60 degrees to the surface at a distance of 1 to 12. inches (3 to 8 preferred). The pressure at which the air impinges on the surface is about 0.1 to 3, and preferably about 0.25 to 2', pounds per square inch. Air cleaning may be applied for several seconds or more until no additional loosely held particles are removed. The remaining powder should be sufficiently adherent to resist removal by moderately forceful wiping or other reasonably abrasive action.

Either before or after the deposition of the light-absorbing pigment particles to the faceplate, groups of stripes, bars or dots of red-emitting, green-emitting and blueemitting cathodoluminescent materials are deposited onto the surface of the faceplate by conventional means. For example, after the deposition of the light-absorbing pigment material in the predetermined phosphor free areas, a suitable negative-acting resist material such as dichromated polyvinyl alcohol can be applied to the faceplate. The dichromated colloid may contain a suitable redemitting, green-emitting or blue-emitting phosphor. Alternatively, a suitable phosphor may be appiled to the surface of the dichromated colloid after the formation of the light-sensitive layer. In either case, the light-sensitive colloid is exposed to light to harden the colloid in the exposed areas and the unexposed areas are Washed out. This process, as explained above, is repeated a total of three times using different phosphors and differently oriented light source thereby providing a multitude of adjacently related color triads and light-absorbing pigment in the phosphor free areas. As indicated above, the light-absorbing pigment layer may be applied prior to the application of the phosphors or after the application of one or more phosphors. After the phosphors and light-absorbing pigment are deposited in image-wise configuration, the faceplate is fired, either before or after assembling the tube, to remove all the organic material on the surface of the faceplate and fuse any unfused phosphor or light-absorbing pigment to the surface of the faceplate.

When powder particles comprising a light-absorbing pigment are applied to the faceplate prior to one or more of the color-emitting phosphors, it is sometimes desirable to treat the light-absorbing pigment image in a suitable manner to render the light-absorbing pigment image impervious to the effects of solvents or other material necessary for depositing said phosphors. In some cases it may be desirable to apply isolating layers between the lightabsorbing pigment layer and phosphor layers. For example, when employing one of the preferred waterinsoluble positive acting light-sensitive layers for depositing the light-absorbing pigment, and isolating layer, such as polyvinyl alcohol, can be deposited on top of the lightabsorbing pigment layer prior to the application of the negative-acting sensitive layer. If desired, the isolating layer can be tanned to an infusable state by employing a dichromated colloid, such as dichromated polyvinyl alcohol or gelatin, and exposing the layer to actinic radiation tanning the isolating layer.

In other cases, it may be desirable to fuse the lightabsorbing pigment particles to the surface of the faceplate prior to the application of negative-acting lightsensitive layers. For example, a carbon-black vinyltoluenebutadiene copolymer developing powder can be fused to the surface of the faceplate with organic vapors, such as ethylene dichloride, or by heat. Alternatively, the lightabsorbing pigment particles can be fused to the faceplate by firing prior to the application of the negative-acting light-sensitive layer. Firing removes all the organic material from the surface of the faceplate and fuses the lightabsorbing pigment particles to the faceplate in proper image-Wise configuration. All of these techniques render the light-absorbing pigment pattern impervious to the effects of solvents or other materials necessary for deposing the cathodoluminescent materials in image-wise configuration.

The following examples are illustrative and should not be construed as limting the scope of our invention.

EXAMPLE 1 One and one-quarter gram Staybelite Ester v# (partially hydrogenated rosin acid esters of glycerol), 0.25 gram benzil and 0.25 gram 4-methyl-7-dimethylaminocoumarin, dissolved in 100 ml. 1,1,1-trichloroethane, is applied to the concave surface of a cleaned faceplate by spraying upwardly to the faceplate forming a Z-micron light-sensitive layer. After drying under ambient conditions, the shadow mask is then fastened to the faceplate and the faceplate exposed through the shadow mask to light rays for about 180 seconds from a point light source approximating the location, relative to the support, that the electron gun associated with the green-emitting phosphor will occupy in the finished tube. The faceplate is then exposed to light for about 180 seconds from a point light source approximating the location, relative to the support, that the electron guns associated with the blue-emitting and red-emitting phosphors will occupy in the finished tube. After the three exposures, the areas to be occupied on the surface of the faceplate by the phosphors have been rendered non-powder receptive. The unexposed areas of the faceplate are developed in a room maintained at 75 F., and 50% relative humidity by rubbing a cotton pad bearing graphite particles of from about 1 to 40 micron diameter along the largest axis across the faceplate. The graphite particles are embedded in the unexposed areas by rubbing the cotton pad back and forth over the light-sensitive layer using the same force as in ultrafine finishing of wood surfaces. Excess graphite is removed from the light-sensitive layer by impinging air at an angle of about to the surface until the surface is substantially free of graphite particles. The faceplate is then wiped with a fresh cotton pad resulting in a discrete graphite image simulating the non-phosphor areas of the faceplate.

A water-alcohol resist solution of polyvinyl alcohol sensitized with ammonium dichromate is applied to the faceplate by spraying upwardly to the faceplate forming a thin tacky coating on the surface of the faceplate. A green phosphor, silver active zinc cadmium sulfide, in a powdered form, is then evenly deposited on the layer of tacky coating by a dusting operation of the type described in US. Pat. No. 3,380,826. If desired, the phosphor and the sensitized polyvinyl alcohol may be applied to the faceplate together in the form of a slurry. The phosphor containing resist layer is then air dried. The shadow mask is again fastened to the faceplate and the faceplate exposed to the shadow mask for about eight to twelve minutes from a discretely positioned point light source simulating the position, relative to faceplate, that the electron gun associated with the green-emitting phosphor will occupy in the finished television tube. After exposure, the unexposed areas of sensitized polyvinyl alcohol containing phosphor is removed by washing the faceplate with water for a period of three minutes which expeditiously removes the unexposed and unhardened portion of the polyvinyl alcohol and phosphor from the mask-shadowed areas.

The blue-emitting phosphor and the red-emitting phosphor are deposited on the faceplate in substantially the same manner as the green-emitting phosphor utilizing the same dichromated polyvinyl alcohol sensitizer. In each case, the point light sources is located in a position, relative to the faceplate, simulating the position of the appropriate electron gun in the finished television tube. Typically, the exposure time for the blue-emitting phosphor is approximately 7 to 10 minutes and the exposure time for red-emitting phosphor is about 25 minutes.

The tri-color television tube faceplate fabricated in this manner has discrete areas of red-emitting, blue-emitting and green-emitting cathocloluminescent materials and black areas filling the interstices between the various cathodoluminescent materials. The faceplate can then be processed in typical manner such as by aluminizing and then firing the faceplate to volatilize all organic material and fuse the graphite and phosphors to the faceplate.

EXAMPLE 2 Example 1 is repeated with essentially the same results except that the Staybelite Ester #10 light-sensitive solution is replaced with a sensitizer containing 5 grams of the ethanol insoluble fraction of soybean lecithin and 0.2 gram benzil dissolved in m1. hexane.

EXAMPLE 3 Example 1 is repeated with essentially the same results except that the graphite developing powder is replaced with the vinyltoluene-butadiene-Neo Spectra carbon black developing powder described in the body of the specification and the vinyltoluene-butadiene carrier is fused to the surface of the substrate with trichloroethylene vapors before the application of the first light-sensitive polyvinyl alcohol solution. Essentially the same results are obtained by replacing the vinyltoluene-butadiene-Neo Spectra carbon black developing powder with Xerox toner and fusing with heat.

EXAMPLE 4 Example 1 is repeated with essentially the same results except that the light-sensitive Staybelite ester layer is applied to the faceplate after the deposition of the threecolor-emitting phosphors to the surface of the faceplate.

EXAMPLE 5 Example 1 is repeated with essentially the same results except that the graphite developing powder is replaced with (a) black manganese dioxide and (1)) black ferric oxide having particle sizes of about 1 to 40 microns along the largest diameter.

EXAMPLE 6 Example 1 is repeated with essentially the same results except that an isolating layer is applied to the developed graphite image before the application of the first sensitizer for the first phosphor. In this case, a dichromated polyvinyl alcohol layer is applied and tanned by uniform exposure of the whole layer to ultraviolet light.

EXAMPLE 7 Example 1 is repeated with essentially the same results except that the Staybelite Ester #10 light-sensitive solution is replaced with a sensitizer solution containing .64 gram of Staybelite Ester #10, .16 gram benzil and .096 gram 4-methyl 7 dimethylaminocoumarin dissolved in 100 m1. 1,1,l-trichloroethane.

EXAMPLE 8 Example 1 is repeated with essentially the same results except that the Staybelite Ester #10 component of the stabilizer employed in Example 1 is replaced with an equal weight concentration of (1) abietic acid, (2) Staybelite resin (partially hydrogenated rosin acids), (3) Staybelite Ester #5 (partially hydrogenated rosin ester of glycerol).

EXAMPLE 9 Example 1 is repeated with essentially the same results except that the Staybelite Ester #10 solution employed in Example 1 is replaced with 1.25 grams Staybelite Ester #10 and 0.25 gram benzil, dissolved in I OO ml. hexane.

Since many embodiments of this invention may be made and since many changes may be made in the embodiments described, the foregoing should be entered as illustrative only and our invention is defined by the claim appended hereafter.

We claim:

1. In the process of forming color television tube faceplates the improvement which comprises (1) coating a cathode ray tube faceplate with a solid,

positive-acting, light-sensitive organic layer containing no conjugated terminal ethylenic unsaturation of from 0.1 to 40 microns thickness, said layer being capable of developing a R,,,, of 0.2 to 2.2 and com prising at least one film-forming organic material selected from the group consisting of esters of internally ethylenically unsaturated acids and internally ethylenically unsaturated acids;

(2) exposing said light-sensitive organic layer in predetermined areas, corresponding to the predetermined cathodoluminescent areas of the faceplate, to actinic radiation in image-receiving manner to render the exposed areas non-powder receptive;

(3) applying to said organic layer, free flowing powder particles comprising at least one light-absorbing pigment, said free flowing powder having a diameter along at least one axis of at least about 0.3 micron but less than 25 times the thickness of said organic layer;

(4) while the layer is at a temperature below the melting point of the powder particles and of the organic layer, physically embedding said powder particles as a monolayer in the stratum at the surface of said light-sensitive layer to yield an image having portions varying in density in proportion to the exposure of each portion; and

(5) removing non-embedded particles from said organic layer to develop a discrete pattern of powder particles comprising at least one light-absorbing pigment.

References Cited UNITED STATES PATENTS 3,428,454 2/ 1969 Angelucci, Jr. 96-36.1 3,365,292 1/1968 Fiore et al 9636.l 2,842,697 7/ 1958 Bingley 3l3--92 3,236,647 2/1966 Philpot 96-34 3,146,368 8/1964 Fiore et al 9636.'1 3,429,731 2/ 1969 France et a1. 1l733.5 CM

NORMAN G. TORCHIN, Primary Examiner E. C. KIMLIN, Assistant Examiner US. Cl. X.R.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTIQN Patent N 3,676, 127 Dated .Julv IL 1972 lnventofls) Thomas F. Protzman and William H. Magidson It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 3, line 20, for "pattern When" read ---pattern. When-- Column 3, lines 59 & 60, for "non-eceptivity" read ---non-receptivity--- Column 3, line 75, for "receptice" read ---receptive-- Column 4, line 40, for "senstiive" read ---seneitive--- Column 5, line 18; for "state, background cleared (under" read ---state (background cleared) under Column 6, line l2gfor "naphanates" read --napthanates--- Column 6, line 55, for "RLS-RHF" read --RLS-PHIF--- Column 10, line 22, for "appiled" read ---applied-- Column 10, lines 73 & 74, for "deposing" read ---depositing--- Signed and sealed this 23rd day of January 1973.

(SEAL) Attest 2 EDWARD M FLETQHERJR. ROBERT GOT'TSCHALK Arresting Offlcer Commissioner of Patents FORM PC4050 (169) USCOMM-DC 60376-P69 I U.S, GOVERNMENT PRINTING OFFICE: I969 0-355-334 Column 4, line 28, for "light-sensitive is" read ---light-sensitive layer 18-- 

